Whoever said the underworld was a bad, scary place never visited some of these spectacular, cool caves! Formed over thousands, in some cases millions of years, these formerly hidden natural wonders are finally revealing their beauty to those who always thought heaven was someplace above.

Mammoth Cave, Kentucky, USA

Mammoth Cave is one of the oldest and most well-known cave complexes in the USA. It’s also the longest cave system in the world with 365 miles of subterranean passageways. Having been made a national park in the summer of 1941, Mammoth Cave was discovered by American settlers in the late 18th century but was known to local native tribes for thousands of years. Highlights of Mammoth Cave include a giant sinkhole called Cedar Sink, and rather self-descriptive features dubbed Grand Avenue, Frozen Niagara and Fat Man’s Misery.

Lascaux Caves, France

The cave complex at Lascaux, in the Dordogne département of southwestern France, host some of the most magnificent prehistoric cave paintings yet discovered. Rendered in natural pigments and estimated to be 16,000 years old, the many hundreds of images in the caves depict some of the Ice Age creatures that were sources of fascination – and food – for the early modern humans who inhabited the area.

The largest images located in the spectacular Great Hall of the Bulls measure up to 17 feet in length! Though we all can enjoy these incredibly lifelike depictions of paleolithic life by way of the Internet, it’s unfortunate that the caves themselves are now virtually off limits to tourists and even researchers due to a destructive fungus that has attacked the paintings. Even when removed, the damage is obvious and, at the present time, irreparable.

Galos Salt Caves, Chicago

Deep beneath Jolly Inn Banquets in Portage Park, Chicago, colored lights illuminate a scene few would expect to set their sights upon. Once an East European secret, the benefits of salt cave siestas have arrived in suburban Chicago. At Galos Caves visitors relax on incongruous lawn chairs, surrounded by salt stalactites and breathing in salt-saturated air while recorded seaside sounds soothe the psyche.

So-called “salt therapy” has legions of adherents who abide by the healing properties of natural salt. Whether it’s the salt itself, the iodine compounds within it or just the relaxing atmosphere inside a salt-lined cave, who can say? Well, owner Ewa Chwala can say – watch her do just that in the following video:

Carlsbad Caverns, New Mexico, USA

Carlsbad Caverns is perhaps the most spectacular “classic” natural cave complex in the USA. Discovered accidentally by Jim White in the late 1890s, the cavern complex includes the Big Room, the second-largest cave chamber in the world. This huge, echoing natural limestone chamber is nearly 4,000 feet (1,219 meters) long, 625 feet (190.5 meters) wide and 350 feet (107 meters) high. Unlike many limestone caves, Carlsbad Caverns was carved out not by underground streams or mild carbolic acid but by strong sulfuric acid formed due to the close proximity of oil and gas deposits.

Young local cowboy Jim White discovered Carlsbad Caverns from a distance when he espied from horseback what appeared to be a “volcano” of bats spiraling out from the cave entrance. At its peak, the population of bats residing in Carlsbad Caverns was estimated to be in the millions.

Then there is the oddly named Erebus Ice Tongue, a glacier that flows down the mountain’s flanks and into the frigid Ross Sea where interaction with waves and sea ice creates temporary ice caves of stunning beauty.

Kartchner Caverns, Arizona, USA

Kartchner Caverns, which runs for over 2 miles beneath the desert sands around Benson AZ, was sealed off from the surface for about 200,000 years until one day in 1974, Randy Tufts and Gary Tenen became the first human beings to set foot inside. The cave system, which was designated Kartchner Caverns State Park in 1999, is exceedingly fragile and its existence was kept secret from all but a few until proper guardianship could be put in place to protect the exquisite formations inside.

The spindly formation above, called Soda Straws, is composed of hollow tubes that incessantly drip from the cavern ceiling. Each drop deposits a minuscule amount of minerals onto the end before falling to the cave floor. Considering that each “straw” grows by just 1/10 of an inch per CENTURY and the longest straw in the cavern is just over 21 feet long, well, you could do the math but I’ll make it easy by saying the Kartchner Caverns straws have been growing undisturbed for a good couple hundred thousand years!

Thylacoleo Caves, Australia

In 2002, an expedition from the Western Australian Museum set out to investigate reports of large skeletons in several caves out in the country’s forbidding desert wasteland, the Nullarbor Plain. Among the remains of dozens of extinct Australian megafauna dating back over 500,000 years were the first complete skeletons of Thylacoleo Carnifex – the Marsupial Lion – ever discovered.

Thylacoleo must have been a terrifying predator to behold, and having one drop in on you while exploring an Australian desert cave would rate rather high among any caver’s list of “what’s the worst that could happen”.

Cave Of The Swallows, Mexico

At 1,200 feet deep, the Cave Of The Swallows (Sotano de las Golondrinas, in Spanish) in central Mexico is deep enough to, er, swallow the Empire State Building. It’s also conical in cross section with the base wider than the top. The cave was only explored recently, in the 1960s.

Here’s a MUST SEE video narrated by David Attenborough showing what have to be the world’s most insane BASE jumpers leaping into the Cave Of The Swallows. Once you’ve done this (and lived), what else is there?

Cave Bacon

No, not Bacon Cave, Cave Bacon… because face it, what self-respecting internet posting these days doesn’t pay homage to that most versatile (and delicious) member of the Pork food group? In any case, “cave bacon” is another, tastier word for layered flowstone formed by the incremental deposition of water-borne minerals along a repeated route. Variations in surface rainfall, mineral balance and other hydrological cum speliological phenomena can affect both the speed and the content of the water moving over the flowstone, leading to layering effects that remind some (heck, ALL) of bacon.

Imagine falling into a cave and, after several fruitless, foodless days have passed, finding THIS hanging over your head? Found in Kentucky’s Diamond Caverns, the calcite drapery formation above stimulates both imaginations and appetites along the New Discovery Passage.

Cave Of Crystals, Mexico

One of the world’s most magnificent caves is also one of the newest to be discovered. In April of 2000, miners at the Naica Mine in Chihuahua, Mexico, stumbled onto a vast, water-filled cave while exploring for lead and zinc. Upon pumping out the mineral-rich, extremely hot water from the underground space, the miners were amazed to find a fantastic lattice of gigantic Selenite crystals measuring up to 40 feet long and weighing as much as 55 tons!

Since the hot supersaturated solution flooding the Cave Of Crystals (or Cueva de los Cristales in Spanish) has been drained, the crystals will not grow any larger. On the bright side, the cave’s 43°C (109°F) plus temperature and 90 to 100 percent humidity ensures that unprotected intruders won’t stay long.

Through the modern technological marvels of video and photography, Earth’s deepest, darkest secrets are at last being revealed. In the case of these truly amazing caves, however, exposure only magnifies their mystery and wonder!